Growth and Nutrient Accumulation and Distribution in Grain Sorghum. I. Dry Matter Production and Ca and Mg Uptake and Distribution

Calcium and magnesium have been found deficient in grain sorghum [Sorghum bicolor (L.) Moench] in some areas. To conduct fertility trials and interpret plant tissue nutrient analyses, we must first understand the growth and nutrient uptake and distribution patterns of the plant. Studies were conducted to investigate growth and Ca and Mg uptake and distribution in grain sorghum throughout its growth cycle. Two grain sorghum hybrids (‘RS 610’ and ‘RS 702’) were planted at the Kansas State University Agronomy Farm, Manhattan, Kan., in 1970 and 1971. Weekly samples were analyzed for Ca and Mg in the plant parts. Dry matter production and Ca and Mg uptake were similar in both hybrids, although a larger proportion of dry matter and Ca and Mg were distributed in vegetative portions of RS 702 than in RS 610. Environmental factors affected growth and nutrient uptake both years, but patterns were similar. Calcium and Mg concentrations varied among plant parts, and concentrations within a plant part were not constant throughout sorghum's growth cycle. Plant-part nutrient concentrations generally were high early in the growth cycles and decreased as the plants reached maturity, except that Ca content in leaf blades increased with maturity. Whole plant Ca and Mg concentrations decreased almost linearly throughout each growing season. Calcium and Mg distributions in plant parts were not proportional to dry matter distribution. Only a small percentage of the plant's total accumulated Ca was in the grain at maturity, when the grain accounted for nearly half of the total plant weight. There was evidence of translocation of Mg from culms to developing grain, but Ca seemed to be immobile. Calcium and Mg uptake preceded dry matter production, and Ca was generally taken up more rapidly than Mg during vegetative growth. When vegetative growth had been completed, more than half of the plant's total Ca and Mg uptake had occurred.